Remove ipproto member of packet_info.

All situations can be handled with "shimmed" dissector functions.

Change-Id: Ic85483b32d99d3270b193c9f6b29574d8fad46a8
Reviewed-on: https://code.wireshark.org/review/5327
Reviewed-by: Michael Mann <mmann78@netscape.net>
Petri-Dish: Michael Mann <mmann78@netscape.net>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Alexis La Goutte <alexis.lagoutte@gmail.com>